This invention relates generally to the formation of positive resist masks using high energy radiation, and more particularly to the solvent development of electron irradiated acrylate polymer resist layers.
The formation of positive resist masks from layers of radiation degradable acrylate polymers is described, for example, by Haller and Hatzakis in U.S. Pat. No. 3,535,137 and by Hatzakis in U.S. Pat. No. 4,087,569. A radiation degradable polymer layer is coated on a substrate and is subjected to patternwise exposure by high energy radiation such as, for example, x-rays, nuclear radiation, and electrons. The irradiated regions of the polymer suffer a decrease in molecular weight and, therefore, become more rapidly soluble. A developer is then used to preferentially remove the irradiated portions of the layer. The substrate is then subjected to an additive or subtractive process, such as metallization or etching, with the remaining portions of the resist layer acting to protect the substrate.
It is possible to employ developers which attack only the radiation exposed portions of the resist layer, and which leave the unexposed portions almost intact. However, it has been found that higher process speeds can be obtained if a solvent is employed which attacks both the exposed and unexposed portions of the resist layer, but which attacks the exposed portion at a higher rate. In order to further speed up the resist mask formation process, developing techniques which speed the development of the exposed portions of the resist, particularly when using higher molecular weight materials, are desirable. One such technique is described in U.S. Pat. No. 4,078,098, where water is added to ketone developers.
It has been observed that different lots of an organic solvent developer often dissolve the resist polymer at much different rates, which makes it difficult to obtain consistently satisfactory resist layer development.
This problem can also result from contamination of the developer during use. For example, the ethylene glycol monoethylether (2-ethoxyethanol) and water developers, which are described in the IBM Technical Disclosure Bulletin article, "Noncracking Developers" by Cortellino, Vol. 19, No. 4, page 1216, September 1976, give dissolution rates which can vary by over 200 A per minute.